The present invention relates to a directional coupler, a high frequency circuit module comprising the same directional coupler and a wireless communication system comprising the same high frequency circuit module, and particularly to the technique that can effectively be adapted to the wireless communication technology to realize the communication under the stable output of a high frequency power amplifier controlled with high accuracy.
In a transmitting side output stage of a transmitter of wireless communication equipment (mobile communication equipment) such as a mobile telephone set and a hand-held telephone set or the like, an amplifier comprising in the multiple stages a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and a GaAs-MES (Metal Semiconductor) FET or the like is used.
For the hand-held telephone set, a system is already established so that the communication is performed by varying an output depending on the ambient environment with a power control signal transmitted from a base station considering the operational environment and thereby any interference is never generated against the other hand-held telephone sets.
For example, in view of avoiding the interference against the other systems, the power control signal is transmitted from the base station of a digital hand-held telephone system to the hand-held terminals (hand-held telephone sets) in order to provide the minimum output required for the communication. At the inside of a terminal utilizing a higher frequency power amplifier comprising FET such as MOSFET or the like, a microcomputer of the baseband unit monitors the power control signal transmitted from the base station and an output of the high frequency power amplifier to adjust the output power by changing a power control signal (Vapc) to be applied to the control terminal of the high frequency power amplifier.
This high frequency power amplifier is described in xe2x80x9cThe Nikkei Electronicsxe2x80x9d, Jan. 27, 1997, p115 to p126, published by the Nikkei BP Co., Ltd. This reference reports the standard system of the 900 MHz Band Cellular System Hand-Helt Telephone System in the North America and the GSM (Global System for Mobile Communications) system in Europe.
Moreover, xe2x80x9cThe Hitachi Reviewxe2x80x9d, Vol. 79, No. 11 (1997), P63 to P38, published by the Hitachi Review Co., Ltd. reports an analog signal processing IC of high frequency unit for digital cellular standards xe2x80x9cGSM/EGSMxe2x80x9d. This reference discloses a block diagram for detecting an output of the high frequency power amplifier with a directional coupler and for controlling a power amplifier module with a power detection signal.
A directional coupler is described, for example, in the xe2x80x9cBasic Items and Applications of a Microwave Circuitxe2x80x9d, Jul. 10, 1997; P191 to P193, published by the General Electronics Publication Co., Ltd. This reference reports a distributed coupling type directional coupler.
On the other hand, xe2x80x9cThe Electronic Materialsxe2x80x9d, April, 1999, P91 to P95, published by the Industrial Investigation Society reports a ceramics-laminated low-pass filter and a directional coupler for 1608 type mobile communication. These low-pass filter and directional coupler are formed as the discrete parts.
In the hand-held telephone system, base stations transmit, to the hand-held terminals (hand-held telephone sets) the signal (power control signal) to control the transmission power to provide the minimum output required for communication. In the hand-held terminals, a high frequency power amplifier of the output stage in the transmitting side is controlled with an APC (Automatic Power Control) circuit operating based on such control signal. Namely, the high frequency amplifier is controlled to provide the output required for communication. To realize such control operation, a circuit for detecting the power of the power amplifier is required.
A directional coupler is used for detecting an output of the high frequency power amplifier and in addition employs a method of comprising a discrete directional coupler as an external part and a structure to form, through direct depiction, a part corresponding to a coupler on a dielectric material substrate based on the concept of xcex/4 line.
That is, the aforementioned reference (Basic Items and Applications of the Microwave Circuit) discloses a structure where a conductor pattern is provided at one surface of the dielectric material substrate as one of the directional couplers and a ground conductor is also provided at the rear surface. In this specification of the present invention, this structure is called a parallel type directional coupler. In this parallel type directional coupler, the conductor pattern is formed as the distributed coupling type parallel two lines. Namely, the main line as the transmission path and the sub-line as the line for detection are extended in the width of the same size for the predetermined distance in the constant interval.
Moreover, one of the other directional couplers disclosed has a structure that two strips are formed by overlapping the main line and sub-line within the dielectric material via the dielectric material layer. In this specification, this structure is called an overlapping type directional coupler. This overlapping type directional coupler also has the structure that the main line and sub-line of the width in the same size are also extended for the predetermined distance with a constant interval therebetween.
However, in these directional couplers, the line width is equal in the main line (transmission line) and sub-line (detection line). Therefore, particularly in the case of the overlapping type directional coupler, if the sub-line is deviated for the main line, an output value of the directional coupler will be changed easily. As a result, when the high frequency circuit module such as a high frequency power amplifier (high frequency power amplifier module) is controlled with this detection signal, it becomes difficult that an output of the high frequency circuit module is controlled with higher accuracy. Therefore, a wireless communication system comprising such high frequency circuit module has come to have a fear for disabling stable communication.
An object of the present invention is to provide a directional coupler that can detect a transmission output of a main line with higher accuracy.
Another object of the present invention is to provide a high frequency circuit module comprising a directional coupler that can detect an output with higher accuracy.
The other object of the present invention is to provide a wireless communication system assuring stable a communication by monitoring an output with higher accuracy.
The aforementioned and the other objects and novel characteristics of the present invention will become more apparent from the description of this specifications and the accompanying drawings thereof.
The summary of the typical inventions of those disclosed in the resent application will be briefly explained as follows.
(1) A directional coupler includes a main line forming the transmission line and a sub-line forming the detection line which are different respectively in the line width. For example, the width of the main line is wider than the sub-line. In the overlapping type directional coupler, both side edges of the sub-line are located, in the main line and sub-line that are overlapped with each other, at the inside of both side edges of the main line.
(2) In the high frequency circuit module comprising an amplifying system comprising a plurality of stages of the amplifying stage including at least the initial stage and the final stage and a directional coupler for detecting an output of the final stage of the amplifying system, the line width of the main line forming the transmission line of the directional coupler is wider than the sub-line forming the detection line. The directional coupler is of the overlapping type and both side edges of the sub-line, in the main line and sub-line that are mutually overlapped with each other, are never extruded to the outside from both side edges of the main line and are located within the internal side of the main line. An impedance of the main line is smaller than that of the sub-line.
(3) A high frequency circuit module comprises a amplifying system comprising a plurality of stages of amplifying stages including at least the initial stage and final stage, a directional coupler for detecting an output of the final stage of the amplifying system and an output control circuit for receiving a power detection signal and a power control signal detected with the directional coupler and supplying the power control signal to each amplifying stage. The width of the main line forming the transmission line of the directional coupler is wider than that of the sub-line forming the detection line. The directional coupler is of the overlapping type and both side edges of the sub-line, in both main line and sub-line that are overlapped with each other, are never extruded to the outside of both side edges of the main line and are located within the inside thereof. An impedance value of the main line is smaller than that of the sub-line.
(4) A high frequency circuit module comprises an amplifying system comprising a plurality of stages of the amplifying stage including at least the initial stage and final stage, a directional coupler for detecting an output of the final stage of the amplifying stage, an output control circuit for receiving a power detection signal and power control signal detected with the directional coupler and supplying the power control signal to each amplifying stage, a filter connected to the final stage of the amplifying system and an antenna switch circuit connected to the filter. Line width of the main line forming the transmission line of the directional coupler is wider than that of the sub-line forming the detection line. The directional coupler is of the overlapping type and both side edges of the sub-line is never extruded, in the main line and sub-line that are overlapped with each other, to the outside from both edges of the main line and are located within the inside thereof. An impedance value of the main line is smaller than that of the sub-line.
(5) In the high frequency circuit module in any one of the structures of items (1) to (4), a plurality of stages of the amplifying systems are provided.
(6) In the structures of items (1) to (5), the main line is narrower than the sub-line. Namely, the high frequency circuit module comprising an amplifying system comprising a plurality of amplifying stages including at least the initial stage and final stage and a directional coupler for detecting an output of the final stage of the-amplifying system and the width of the main line forming the transmission line of the directional coupler is smaller than that of the sub-line forming the detection line. The directional coupler is of the overlapping type and both side edges of the main line, in the main line and sub-line that are overlapped with each other, are located in the internal side of both side edges of the sub-line. Impedance of the main line is larger than that of the sub-line. Moreover, a matching circuit for impedance matching is provided between the main line and the final amplifying stage, while a matching circuit for impedance matching against a device for detecting a current of the sub-line is provided between the sub-line and an output terminal of the sub-line.
(7) A wireless communication system comprises a high frequency circuit module of any structure of items (1) to (6).
According to the means of item (1), (a) the main line becomes wider than the sub-line and thereby loss of the main line can be reduced, and (b) in the case of the overlapping type directional coupler, since both side edges of the sub-line are never extruded to the outside of both side edges of the main line and located in the internal side thereof, the total area of the line width of the sub-line can surely be provided are opposed to the main line and thereby highly accurate power detection can be performed.
According to the means of item (2), (a) since both side edges of the sub-line are never extruded to the outside from both side edges of the main line and are located within the internal side thereof in the overlapping type directional coupler in the high frequency circuit module and the main line width is wider than the sub-line width, the sub-line is surely placed opposed to the main line in the total line area and thereby the power can be detected with higher accuracy, and (b) since the line width of the main line can be set larger than that of the sub-line, the line width of the main line can be selected freely. Accordingly, from the point of view of the high frequency circuit module to be built into a wireless communication system, the main line can be comprised as a part of the matching element of the module, resulting in the parts saving effect and loss reducing effect.
Even in any high frequency circuit module of those in the items (3) to (5), the effect similar to that of the module having the means of item (2) can also be attained.
According to the means of item (6), in the directional coupler, (a) since the width of the main line is set narrower (shorter) than that of the sub-line, the coupling coefficient increases, whereby the overlapping length (coupling length) between the main line and sub-line can be set short and reduction in size of the high frequency circuit module can be attained and moreover since the coupling length can be shortened, the loss of signal passing the main line can also be reduced, and (b) since both side edges of the main line is never extruded to the outside from both side edges of sub-line and are located in the inside thereof, the total line width can surely be provided opposed to the main line and thereby highly accurate power detection can be performed.
According to the means of item (7), since the power detection of the high frequency circuit module can be performed in higher accuracy, high precision output control is possible for the high frequency circuit module and thereby stable communication can be realized.